1. Field of the Invention
The invention relates to an arrangement for current limiting having a superconducting cable which is arranged in a cryostat which has an outer wall which comprises two metallic tubes which are arranged concentrically with respect to one another and between which vacuum insulation is incorporated, and which surrounds a free space for a coolant to pass through, in which free space the superconducting cable is arranged (EP 1 681 731 A1).
2. Description of Related Art
In modern technology, a superconducting cable has electrical conductors composed of a composite material which contains ceramic material which changes to the superconducting state at sufficiently low temperatures. The electrical direct-current resistance of a correspondingly designed conductor is zero when the cooling is adequate, provided that a specific current level, the critical current level, is not exceeded. Suitable ceramic materials, are, for example, YBCO (yttrium barium copper oxide) or BSCCO (bismuth strontium calcium copper oxide). Sufficiently low temperatures to change a material such as this to the superconducting state are, for example, between 67 K and 110 K. Suitable coolants are, for example, nitrogen, helium, neon and hydrogen or mixtures of these substances.
An arrangement for current limiting as described initially can be incorporated as a type of fuse into any desired cable run or else a switchgear assembly as a transmission path, via which or in which currents of greater or lesser magnitude can be transmitted. The aim is to prevent considerable damage from occurring thereto in the event of a short on the transmission path. A considerable increase in the electrical impedance of the arrangement which occurs in the event of a short triggers a mechanism by means of which the transmission path is disconnected from the supply current source. Once the reason for the short has been rectified, the transmission path can be switched on again without having to change the current-limiting arrangement at all.
EP 1 681 731 A1 as mentioned initially, describes a superconducting component for current limiting. This comprises a cylindrical support composed of superconducting material, around which a superconducting conductor is wound. A normal conductor is connected in parallel with this. A plurality of such components are connected electrically in series in order to produce a current limiter.